In general, there are various kinds of secondary batteries, such as a nickel cadmium battery, a nickel hydride battery, a lithium ion battery, and a lithium ion polymer battery. Such secondary batteries have been used in large-sized products that require high output, such as an electric vehicle and a hybrid electric vehicle, a power storage device for storing surplus power or new and renewable energy, and a backup power storage device. Secondary batteries also used in small-sized products, such as a digital camera, a portable digital versatile disc (DVD) player, an MP3 player, a personal digital assistant (PDP), a portable game device, a power tool, and an electric bicycle (E-bike).
A lithium secondary battery is charged and discharged through a process in which lithium ions from a lithium metal oxide of a positive electrode are repeatedly intercalated into a negative electrode, such as a graphite electrode, and the lithium ions are repeatedly deintercalated from the negative electrode.
Heat may be generated from such a lithium secondary battery due to a short circuit by external impacts, the overcharge or the overdischarge of the lithium secondary battery. As a result, an electrolyte may be decomposed into gas in the lithium secondary battery, and thermal runaway could occur in the lithium secondary battery. These are several aspects for safety of the lithium secondary battery. In particular, the secondary battery may explode for various reasons. In one example, the secondary battery may explode due to an increase in the pressure of air in the secondary battery, which is caused by the decomposition of an electrolyte. Specifically, when the secondary battery is repeatedly charged and discharged, gas may be generated in the secondary battery as the result of the electrochemical reaction between the electrolyte and an electrode active material. The gas generated in the secondary battery increases the pressure in the secondary battery. As a result, the fastening force between parts constituting the secondary battery may be reduced, the external case of the secondary battery may be damaged, a protection circuit of the secondary battery may be operated early, an electrode of the secondary battery may be deformed, a short circuit may occur in the secondary battery, or the secondary battery may explode.
In order to secure the safety of such a battery when the battery is overcharged, overcurrent is prevented from flowing in the battery through the control of electronic parts, whereby the battery is prevented from being overcharged. To this end, a protection circuit, such as a protection circuit module (PCM), may be applied to the battery. Even in the case in which such an overcharge protection circuit, such as a PCM, is applied to the battery, however, it is difficult to sufficiently secure the safety of the battery. In particular, it is necessary for a pouch-shaped battery to be provided with a further improved protection circuit structure in order to more accurately check the swelling of the pouch-shaped battery.
In addition, there has been used a mechanical current interrupt device that physically interrupts the series connection of a battery pack using the pressure generated in the battery due to thermal expansion of the battery when the battery is overcharged in consideration of malfunction of the electronic parts of the battery. Generally, in the current interrupt device of the battery pack, there is widely used a method of physically cutting the series connection of the battery pack through the structure of the battery pack using only the pressure generated in the battery as the battery is expanded when the battery is overcharged in order to interrupt the flow of current in the battery pack. However, a short circuit formation unit that is capable of interrupting the flow of current in a pouch-shaped battery when the volume of the pouch-shaped battery is increased has not been suggested.
Korean Patent Application Publication No. 2016-0129763 (2016, Nov. 9) discloses a lithium secondary battery including a positive electrode plate, a separator, and a negative electrode plate, which are sequentially stacked, an electrode tab extending from one side of each of the positive electrode plate and the negative electrode plate by a predetermined length, and an electrode lead electrically connected to the electrode tab, wherein a welded portion is provided at at least a portion of a region between the electrode tab and the electrode lead under a normal operating condition of the lithium secondary battery and wherein the welded portion is cut under an abnormal operating condition of the lithium secondary battery, for example when the temperature of the lithium secondary battery is high. However, any unit corresponding to a short circuit formation unit for separating two-level concave and convex electrode leads, connected to each other via a conductive adhesive, from each other when the volume of a pouch-shaped battery case is increased is not suggested.
Korean Registered Patent No. 10-1601123 (2016, Mar. 8) discloses a secondary battery including an electrode assembly and a battery case, in which the electrode assembly is provided in a sealed state such that the electrode assembly is isolated from the outside, wherein the secondary battery further includes a first electrode lead, having one end connected to the electrode assembly so as to protrude from the electrode assembly and the other end exposed outward from the battery case, and a second electrode lead, detachably connected to the first electrode lead, the second electrode lead extending from the inside of the battery case to the outside of the battery case so as to be exposed outward from the battery case, and wherein an adhesive portion for coupling the first electrode lead and the second electrode lead is provided outside the battery case. However, any unit corresponding to a short circuit formation unit for cutting an electrode tab and an electrode lead when the volume of a pouch-shaped battery case is increased is not suggested.
Korean Registered Patent No. 10-1614434 (2016.05.02) discloses a battery cell having an overcurrent interrupt function, the battery cell including an electrode assembly, an electrode lead connected to the electrode assembly, the electrode lead including a first metal plate and a second metal plate located so as to be spaced apart from each other by a predetermined gap and an alloy bridge for filling the gap between the first metal plate and the second metal plate, the alloy bridge having a melting point lower than the melting points of the first metal plate and the second metal plate, a cell case for receiving the electrode assembly such that the electrode lead is exposed outward, and a CTR terminal connected between opposite ends of the battery cell for causing a short circuit outside the battery cell when the temperature of the battery cell exceeds a predetermined temperature, wherein the alloy bridge exhibits electrical resistance higher than the electrical resistances of the first metal plate and the second metal plate, and wherein the alloy bridge is located outside the cell case. However, any unit corresponding to a short circuit formation unit for separating two-level electrode leads, connected to each other via a conductive adhesive, from each other when the volume of a pouch-shaped battery case is increased is not suggested.
Korean Patent Application Publication No. 2012-0139590 (2012, Dec. 27) discloses a part for secondary batteries including a lead-free soldering bridge having a melting point of 150 to 300° C., the lead-free soldering bridge being mainly made of tin (Sn) and copper (Cu), and a first metal plate and a second metal plate joined to the lead-free soldering bridge in the state of being spaced apart from each other by a small gap. However, any unit corresponding to a short circuit formation unit for separating two-level electrode leads, connected to each other via a conductive adhesive, from each other when the volume of a pouch-shaped battery case is increased is not suggested.
Japanese Patent Application Publication No. 2011-249128 (2011, Dec. 8) discloses a temperature fuse including a pair of lead conductors opposite each other in the state of being spaced apart from each other in a longitudinal direction, a pair of notches formed in opposite ends of the lead conductors so as to face outward in the longitudinal direction, and a joint for joining the lead conductors by welding the opposite ends of the lead conductors using a low melting-point soluble alloy, wherein the size of each of the notches in the longitudinal direction is set to be equal to or greater than the size of the joint in the longitudinal direction. However, any unit corresponding to a short circuit formation unit for separating two-level concave and convex electrode leads, connected to each other via a conductive adhesive, from each other when the volume of a pouch-shaped battery case is increased is not suggested.
Korean Patent Application Publication No. 2015-0074439 (2015, Jul. 2) discloses a battery overcharge safety device including a battery stack constituted by a plurality of cells, a safety circuit electrically connected to two or more cells of the battery stack, the safety circuit having an interrupting means for selectively interrupting the electrical connection of the cells, and a closed circuit provided between the cells connected to the safety circuit, the closed circuit having a switching means for selectively switching the electrical connection of the cells when the cells swell, wherein the switching means is pushed and turned ON to open the interrupting means of the safety circuit and the electrical conduction between the cells is achieved through the switching means when the cells swell, and wherein the switching means is turned OFF and the electrical conduction between the cells is interrupted when the cells swell further. However, any unit corresponding to a short circuit formation unit for separating two-level concave and convex electrode leads, connected to each other via a conductive adhesive, from each other when the volume of a pouch-shaped battery case is increased is not suggested.
That is, a short circuit formation unit for short-circuiting a pouch-shaped secondary battery when the pressure in the battery increases or when the volume of the battery increases in an abnormal state of the battery, for example in the case in which the battery is overcharged or in the case in which gas is generated in the battery, in order to secure the safety of a pouch-shaped battery and a pouch-shaped secondary battery including the same have not been suggested.